Step valve

ABSTRACT

The invention concerns a valve arrangement installed in a hydraulic system including a housing (17a, 17b) which is provided with two connections (22, 23) and includes a closing element (14) which lies in a neutral position on a valve seat (6). In accordance with the invention, a valve element (11) is provided which has two step valves (15a, 15b), arranged at a distance, each being associated with one flow direction, whose the closing elements (14) are acted upon by a spring force.

BACKGROUND OF THE INVENTION

The invention relates to a valve arrangement of a hydraulic system,constructed as a step valve, including a housing which is provided withtwo pressure connections and has at least one valve seat to which aclosing element is allocated which, in a closed position, has a firstvalve surface which is smaller than a second valve surface, which it hasin a position where the closing element is displaced from the valveseat.

The use of one way valve, also called a non-return value or reliefvalve, is known in hydraulic systems to make a pressure medium flowpossible and to block a return flow. Known valves of this type have aspring actuated closing element which lies sealingly against the sealingseat of the one way valve in its closed position. The construction ofthe valve requires that the opening pressure substantially depends uponthe initial stressing force of the spring and the valve surface actedupon by pressure fluid. In this way, an increasing pressure flowresistance appears with the rise in the flow volume. This property isdisadvantageous for a number of applications.

From DE-A 27 28 486 a type of valve arrangement is known in which aclosing element lies sealing on a housing-side valve seat in the closedposition. The pressurized fluid flows toward the closing element via anentrance in the housing and acts upon a valve surface which is smallerthan a second valve surface which appears after the pressurized fluiddisplaces the closing element from the valve seat. The second valvesurface at the same time corresponds to the diameter of the sphericalclosing element, whereby immediately after lifting the closing elementfrom the valve seat, the flow-through cross section is not yet set up,because the closing element must be guided through a stepped section ofa step boring having a diameter which is only slightly larger than thediameter of the closing element. After a further displacement of theclosing element in a next larger section of the step boring, a newflow-through cross section is set up. The familiar one way valve makespossible an uncontrolled shifting of the closing element in the openposition, whereby this can knock against the housing, which leads to adisadvantageous development of noise.

SUMMARY OF THE INVENTION

The object of the present invention is to minimize the flow-throughresistance for a valve arrangement which is acted upon by pressure fluidin two flow directions, whereby its construction makes an effectivereduction of noise possible.

The object is accomplished by the features mentioned in thecharacterization part of the first claim.

The accomplishment of the objective consists of arranging two stepvalves in a valve element at a distance from each other, each associatedwith one direction of flow, which are correspondingly provided with avalve seat and a spring actuated closing element. The inventive valveelement used in a valve arrangement (which, for example, can be used inconnection with a hydraulic circulation having changing flowdirections), possesses an advantageous degressive opening characteristicof the closing element. This is achieved, since after opening theclosing element, the flow resistance diminishes in comparison to aclosed closing element owing to a larger surface acted upon on theclosing element. In addition to the different surfaces of the closingelement which are acted upon by pressure fluid between the closed andthe open state, a relatively weak spring which displaces the closingelement in the direction of the valve seat brings about a desiredreduction of the flow resistance of the valve element.

Based on this configuration, a higher pressure is necessary for openingthe step valve in comparison with the opened step valve. This mode ofoperation is useful for compensating for pressure pulsations inhydraulic systems through which, for example, pressure fluctuationsoccurring very frequently do not lead to a disadvantageous unwantedopening of the valve. The invention brings it about that the change inthe hydraulically effective surface or in the loss of pressure on thestep valve can be purposefully adjusted as a function of the flowvolume. Advantageously, the pedal feel on the clutch pedal can beimproved by using the step valve in a hydraulically actuated clutch in amotor vehicle.

In an advantageous configuration of the invention, the valve arrangementcomprises two valve seats arranged radially at a distance in a valvedisk, one valve seat being associated with each direction of flow, towhich a closing element is allocated in each case. This compact stepvalve arrangement associated with both flow directions makes adigressive opening possible for both flow directions. Based on thelayout, which is optimized as to construction space, a step valveconstructed in this manner can, for example, be combined with othercomponents of a hydraulic system.

The design of the compression springs, which are arranged with eachclosing body, is provided such that between the open and closed state ofthe closing body there are nearly equal spring forces appear.

For this, a relatively weakly constructed spring is used, which, inconnection with the various valve surfaces on the closing element,supports the desired degressive opening characteristic of the stepvalve.

It is appropriate to use a rotation symmetrically configured componentas a closing element. A closing element in the form of a ball isespecially suitable for this. Furthermore, closing elements configuredas thrust washers can likewise be used which have a diameter gradationwhich is adapted to the diameter gradation of the valve seat. As afurther alternative, a rotationally symmetrical closing element having acylindrical construction form can also be used which is configuredconically on both faces, forming a truncated cone. For reducing themass, the cylindrically shaped closing element may be constructed as ahollow element.

For assuring or intensifying the digressive opening characteristic, itis expedient for the larger valve surface to correspond to one, 1.2 to 5times the value of the valve surface which in the closed step valve isacted upon by pressure medium.

In a further advantageous configuration of the invention, the valve diskhas guide elements for guiding the closing element, which also providethe closing element with a radial guidance in the opened state. Thisway, a disadvantageous noise excitation can be effectively preventedwhich occurs in connection with previous one way valves or step valvesin which the closing element strikes on the housing wall in anuncontrolled manner. At the same time, the radial guide for the closingelement can be constructed in multiple configurations. Preferably, forexample, rods or pins connected in one piece with the valve disk or withthe housing of the step valve are suitable. Furthermore, bushings,sleeves or guiding rods may be positioned in the valve disk or thecomponents surrounding the valve disk for use as guide elements.Alternative guide elements with suitable cross section profiles arefurthermore suitable. The invention provides guide elements which securea guide play which comes to ≦0.1 mm by means of which an exact guidanceof the closing element can be obtained in connection with an effectivesuppression of noise.

The concept of the invention provides in addition for the closingelement to lie on the sealing disk attaining a high degree of sealing inthe blocking state, that is, sealing in the closed state. As a measurefor suppression of noise and assuring optimal sealing, in accordancewith the invention, the sealing seat or valve seat for the closingelement is made of a plastic, especially a polymer material, so thateven a closing element striking upon the sealing seat with a highclosing velocity causes no disadvantageous noise excitation. As analternative, a valve disk made of plastic can be used. As a supportingmeasure, the guide elements can be provided with a coating on the sidedirected toward the closing element, for example a PTFE coating, throughwhich a steel on steel arrangement is avoided, which can have adisadvantageous effect on the noise level.

A defined leakage slit is allocated to the closing element in support ofthe digressive opening character. This leakage slit, which isadvantageously positioned in a guide element, extends over the entireregulating displacement of the closing element. With this measure, flowresistance can be influenced advantageously in the opening phase. Bydimensioning and/or geometrical configuring the leakage slit, which canbe shaped as a function of temperature, viscosity or other in flowdimensions of the pressurized fluids, the course of the characteristiccurve of flow-through resistance can be influenced.

The invention provides at least one lead-off cross section arranged onthe closing element over which a pressure medium flow-through the stepvalve can take place after an axial displacement of the closing element.Introducing recesses at a distance in the wall of the guide element, forexample, offers itself as a lead-off cross section, whereby the lead-offcross section can be constructed as a bore hole or as an elongated slot.In addition to the number, the profiling of the lead-off cross sectioncan also be variably constructed. An axially graded arrangement of thelead-off cross sections toward one another is provided as anadvantageous configuration for influencing the through flow resistancein the area of the greatest volume aperture in accordance with theinvention. Alternatively, a helically running arrangement of thelead-off cross sections is also presented.

It is appropriate to arrange the lead-off cross section or even severallead-off cross sections such that a pressure medium flow can take placefollowing a stroke of the closing element between 0.1 to 2 mm. Throughthis arrangement of the lead-off cross section, small amplitudefluctuations which occur very frequently in the hydraulic system can becompensated for.

As a further measure suppressing the excitation of noise by the closingelement, the invention provides asymmetrically arranged guide elementsas well as lead-off cross sections. For reaching a desired arrangementof the closing element on one or more guide elements in the openedstate, the guide elements have cross sectional areas deviating from oneanother. This way, a directed current is advantageously set up whichpurposefully displaces the closing element in one direction.

A further configuration of the invention provides that the closingelements allotted to a flow direction in any given case have openingpressures deviating from each other. With this, a different openingcharacteristic between the two flow directions can be obtained whenneeded. For achieving deviating opening pressures, the compressionsprings allocated to the closing element can have different springcharacteristic curves. Alternatively, varying the dimensioning of, forexample, the valve surfaces acted upon for opening the closing elementcan be used for achieving divergent opening pressures.

The invention furthermore includes, as an alternative to a spring, usingmagnetic means for obtaining a degressive opening characteristic of theclosing body. Permanent magnets which bring about a force-lockingdisplacement of a closing element made of metal in the direction of thevalve seat are suitable for this. The arrangement of the inventionprovides here that the force of the magnetic means stands in inverseproportion to the distance which is set up between the closing elementand the magnetic means. By using magnetic means, the requirement ofrealizing a step valve optimized as to construction space can be betterrealized since this requires a smaller construction space in comparisonto a compression spring.

The valve arrangement of the invention is suited for installation in ahydraulic system for a hydraulically actuated friction clutch invehicles, which is subjected to the longitudinal vibrations of theinternal combustion engine which are triggered by combustion strokes,and which bring about a bending strain of crank journal and crank arm ofthe crankshaft which are transmitted over the friction clutch to thehydraulic system and which lead to a disadvantageous crawling of theclutch pedal which impairs driving comfort.

As a further area of use for the valve element of the invention, it isappropriate for switchable, hydraulically activatable valve drivemembers for the activation of gas exchange valves in internal combustionmachines. The opening characteristic realizable through the valve of theinvention offers itself especially for use in pressure medium conduitsfor switching tamping tools, and hydraulic valve play compensationelements. Hydraulic clamping devices for tension medium drives as wellas hydraulic steering aid systems are to be viewed as a further area ofapplication of the valve element of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Three embodiments are described in detail below on the basis of sixdrawings, wherein:

FIG. 1 is a cross-section of the principal structure of a step valve ofthe invention;

FIG. 2 shows a valve element in a longitudinal cross-section whichincludes two radially spaced step valves arranged at a distance from oneanother;

FIG. 3 shows a front view of the valve element in accordance with FIG.2;

FIG. 4 shows the valve element in accordance with FIG. 2 insertedbetween two housings to create a damping element;

FIG. 5 shows an alternatively configured damping element to that shownin FIG. 4, with cylindrically constructed closing elements;

FIG. 6 is a diagram of the characteristic curve of the flow-throughresistance of the step valve of the invention in comparison with aconventional one way valve;

FIG. 7 shows a valve element similar to FIG. 3 with an alternatearrangement of the lead-off cross sections of the step valves.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a valve element 1 is depicted in longitudinal section, whichrepresents a one way valve constructed as a step valve 5 and a housing 2which has guide elements 3 pointing in one direction which are joined inone piece with the housing 2 and which are radially arranged around aclosing element 4. Here the closing element 4, which is acted upon bythe force of a compression spring 10 which is mutually braced on ahousing 7, lies on a valve seat 6 formed on the housing 2. The guideelements 3 form a closing element guide while maintaining a narrow guideplay. To obtain a pressure medium current through the step valve 5, thepressure medium pressure acting upon the closing element 4 over thevalve surface "d" displaces the closing element in the direction of thearrow. As soon as the closing element 4 is raised from the valve seat 6,the pressure medium acts upon valve surface "D," which corresponds tothe equator, that is the largest diameter of the closing element 4. Onthe basis of the differences in area between the valve surfaces "d" and"D" and the use of a relatively weak compression spring 10, the flowresistance diminishes with the consequence that the opening speed of theclosing element 4 increases. Immediately after raising the closingelement 4 from the valve seat 6, a portion of the pressure medium canflow off through leakage slit 8. This leakage slit 8, which avoidsdisadvantageous strong pressure grades or transitions, is arranged inthe form of a longitudinal groove in a guide element 3. Upon arriving atsite "A" of closing element 4, that is when the equator area of closingelement 4 passes beyond position "A," the pressure medium can flow offover a lead-off cross section 9a without pressure. With a further shiftof the closing element 4 beyond site "B," an additional amount ofpressure medium is drained off over lead-off cross section 9b. Bychanging the measure of difference "s" between sites "A" and "B,"influence can be exerted on flow-through resistance. Instead of the twostage construction of the lead-off cross sections 9a, 9b in FIG. 1, theinvention likewise provides an arrangement of the lead-off crosssections on the guide elements 3 constructed graded over theirperimeter. A construction of the lead-off cross sections with a helicalconfiguration can be provided alternatively.

Mode of Operation of the Valve Element

A pressure medium current which flows against valve element 1 over thevalve surface "d" (see arrow) acts upon the closing element 4 depictedin FIG. 1. An axial movement of the closing element 4 can take place inthe direction of the arrow if a force resulting from the product of thevalve surface "d" and the pressure of the pressure medium is greaterthan the force of compression spring 10. With a movement of the closingelement 4, which is provided with two valve surfaces "d" and "D" ofdifferent dimensions from each other, an accelerated movement of closingelement 4 is set up after a movement, namely a lifting of closingelement 4 from valve seat 6 owing to the larger valve surface "D" whichcan be acted upon by pressure medium. In connection with this, a portionof the pressure medium is led off over a leakage slit 8 arranged in aguide element 3. An increased pressure medium flow can take placethrough the step valve 5 as soon as the equator of the closing element 4has reached site "A." The largest opening cross section results when theclosing element 4 has passed site "B" and the pressure medium can flowoff over lead-off cross section 9b.

In a further embodiment (FIG. 2 and FIG. 3) of a valve element 11 of theinvention, components in accordance with the first embodiment areprovided with numbers higher by 10, so that, concerning its description,reference can be made to the first embodiment (FIG. 1).

The valve element 11 depicted in FIG. 2 includes two step valves 15a,15b arranged radially at a distance to each other positioned in a valvedisk 12, whereby the valve disk 12 corresponds by its function to thehousing 2 according to the embodiment in FIG. 1. The step valves 15a,15b arranged in an alignment are allocated to one current direction ineach case. The respective arrows indicate in which direction the closingelements 14 can be moved by hydraulic fluid to reach a pressure mediumflow-through. For optimizing flow, valve disk 12 has on the in flow sideof valve surface "d" rounded inlets as well as lead-off cross sections19 which are in any given case constructed as spread radially outwardbeginning from site "A" or "B." As opposed to valve element 1 (inaccordance with FIG. 1), the guide elements 13 are a component of valvedisk 12 which are positioned by means of a boring into valve disk 12.From the front view of the valve element 11 (see FIG. 3), thearrangement of the lead-off cross sections 19 becomes clear which are ineach case arranged circumferentially around the respective closingelements 14 in valve disk 12. This arrangement makes possible a circularaxial grading of the sites "A" by means of which an almost continuousenlargement of the sum of lead-off cross sections is set up.

FIG. 4 depicts a damping element 21 which can be used as a "crawlfilter" for hydraulic operation of a friction clutch of vehicles, andwhich includes two housings 17a, 17b which have a connection 22 or 23,whereby between housings 17a, 17b the valve element 11 in accordancewith FIG. 2 is inserted. To create a unitary assembly, the housings 17a,17b are surrounded in a middle region by a bushing which is providedwith a radially inwardly extending flange on both faces.

In comparison with FIG. 4, an alternatively constructed damping element41 is to be understood from FIG. 5 which provides closing elements 24 ina cylindrical type of construction which are installed in the valve disk32 radially spaced at a distance from each other. On both faces, theclosing elements 24 have truncated cone-like transitions, which on theone side lies on valve seat 26 in the closed state of the valve element31 and in relation to which a compression spring 30 is reciprocallycentered. The construction of the valve element 31 provides for a valvedisk 32 made of plastic in which the lead-off cross sections 29a, 29bare located, and a leakage slit 28a, 28b is assigned to each closingelement 24. Retention fingers formed as one piece with the valve disk 32project axially out of the valve disk 32 to serve as guide elements 33.These guide elements 33 are arranged at a distance to one another aroundthe closing element 24 to guarantee an exact guidance of the closingelement 24 which form the step valves 25a, 25b. The damping element 41furthermore includes the housings 27a, 27b located on both sides of thevalve disk 32 which are surrounded by a sleeve 34 to create a unitaryassembly, and on the end faces is joined in a form-locking manner withthe housing 27a, 27b.

FIG. 6 clarifies in a diagram the course of flow-through resistance ofthe step valve 5 or 15a, 15b of the invention in comparison with aconventionally constructed ball valve in a one way valve construction.Here the flow-through resistance "ΔP" is entered on the ordinate and thevolume flow "V" on the abscissa. The curve plot "a" represents the stepvalve 5 or 15a, 15b and manifests a strongly degressive course, that is,the pressure necessary to open closing element 4, 14 is clearly higherthan the pressure which arises in the opened state in connection withrelatively low flow-through volumes. A rise in pressure takes place as afunction of the flow-through volume. In contrast to this, the curve plot"b" shows the flow-through resistance for a conventionally constructedone way valve with a closing body in the form of a ball in connectionwith which flow-through resistance rises as soon as the one way valvebegins to open.

FIG. 7 shows a front view of the valve element 11, similar to FIG. 3,which differs in that the lead-off cross sections deviate from thearrangement shown in FIG. 3. Each through flow cross section of thevalve disk 12 is provided with two lead-off cross sections 19a which arespaced apart from one another, in which the axial distance to the valveseat 16 (shown in FIG. 2) changes in helical form, as indicated by thedashed lines. Additional straight sided lead-off cross sections 19 arealso included in the valve disk 12. Based on an asymmetrical arrangementof the lead-off cross sections 19, 19a, guide elements 13 which havecross sectional areas which deviate from one another are provided.

Reference Designations

1 Valve element

2 Housing

3 Guide element

4 Closing element

5 Step valve

6 Valve seat

7 Housing

8 Leakage slit

9a Lead-off cross section

9b Lead-off cross section

10 Compression spring

11 Valve element

12 Valve disk

13 Guide element

14 Closing element

15a Step valve

15b Step valve

16 Valve seat

17a Housing

17b Housing

18 Leakage slit

19 Lead-off cross section

20 Compression spring

21 Damping element

22 Connection

23 Connection

24 Closing element

25a Step valve

25b Step valve

26 Valve seat

27a Housing

27b Housing

28a Leakage slit

28b Leakage slit

29a Lead-off cross section

29b lead-off cross section

30 Compression spring

31 Valve element

32 Valve disk

33 Guide elements

34 Sleeve

41 Damping element

We claim:
 1. Valve arrangement for a hydraulic system, constructed as astep valve (15a, 15b; 25a, 25b), comprising a housing (17a, 17b; 27a,27b) that is provided with connections (22, 23) and is provided with avalve element (11, 31) that has two spaced apart step valves (15a, 15b;25a, 24b), each associated with a flow direction, each step valve beingprovided with a valve seat (16, 26) and a spring actuated closingelement (14, 24), whereby the closing element (4, 14, 24) has a firstvalve surface (d) in a closed position which is smaller than a secondvalve surface (D), which appears in a displaced position of the closingelement from the valve seat (6, 16, 26), the two step valves (15a, 15b;25a, 25b) are provided with the valve seats (16, 26) which are radiallyspaced apart in a valve disk (12, 32) and include leakage slits (8, 18,28) arranged along the same axial displacement of the closing elements(4, 14, 24), and the valve disk (12, 32) includes guide elements (13,33) arranged circumferentially about sides of the closing elements (14,24) for guiding the closing elements (14, 24), whereby for actuating theclosing element (14, 24) a compression spring (10, 20, 30) is providedhaving approximately equal spring force between an open and a closedposition of the closing elements (14, 14, 24) to obtain a degressiveopening characteristic for the step valves (15a, 15b; 25a, 25b). 2.Valve arrangement according to claim 1, wherein one of arotationly-symmetrical component and a ball is provided as the closingelement.
 3. Valve arrangement according to claim 1, wherein the closingelement is a rotationly-symmetrical closing element (24) in acylindrical form which has a truncated cone portion on both faces. 4.Valve arrangement according to claim 1, characterized in that the valvesurface (D) corresponds to 1.2 to 5 times the value of valve surface(d).
 5. Valve arrangement according to claim 1, wherein the valve disk(12, 32) has a bushing or casing extending in an opening direction ofthe closing element (14, 24).
 6. Valve arrangement according to claim 1,wherein pegs are provided for guiding the closing element (14, 24) whichare positioned in or are joined in one piece with the valve disk (12,32).
 7. Valve arrangement according to claim 1, wherein the valve disk(12, 32) or a component surrounding the valve disk (12, 32) has pegswhich form the guide elements (13, 33) for the closing element (14, 24).8. Valve arrangement according to claim 1, wherein a measure for a guideplay between the closing element (4, 14, 24) and the guide element (3,13, 33) is ≦0.1 mm.
 9. Valve arrangement according to claim 1, whereinat least one of the valve disk (12, 32) and the valve seat (6, 16) ismade of a plastic or polymer material.
 10. Valve arrangement accordingto claim 1, wherein the leakage slit (8,18, 28) one of a half round,triangular or rectangular shaped contour.
 11. Valve arrangementaccording to claim 1, wherein at least one lead-off cross section (9a,9b; 19; 29a, 29b) is associated with the closing element (4, 14, 24),over which a pressure medium flow through the step valve (5, 15a, 15b,25a, 25b) takes place following an axial movement of the closing element(4, 14, 24).
 12. Valve arrangement according to claim 11, wherein thereare at least two lead-off cross sections (9a, 9b; 19; 29a, 29b) whichare configured axially graded in relation to each other.
 13. Valvearrangement according to claim 11, wherein there are at least twoperipherally arranged lead-off cross sections (19a), whose axialdistance to the valve seat (6, 16) changes in helix form.
 14. Valvearrangement according to claim 11, wherein an axial distance of thelead-off cross sections to the valve seat (6, 16, 26) is provided whichrequires an axial movement of the closing element (4, 14, 24) from 0.1to 2.0 mm to obtain a pressure medium flow.
 15. Valve arrangementaccording to claim 11, wherein the guide elements (13) and the lead-offcross sections (19) are arranged asymmetrically and or havecross-sectional areas deviating from one another to arrive at a desiredarrangement of one or more guide elements (13) for the closing element(14) in an opened state.
 16. Valve arrangement according to claim 1,wherein a step valve (15a, 15b, 25a, 25b) in connection with which theclosing elements (14, 24) are assigned to a flow direction have openingpressures which differ from one another.
 17. Valve arrangement accordingto claim 1, wherein the valve element (11, 31) is used in hydraulicallyactuated friction clutches of motor vehicles.
 18. Valve arrangementaccording to claim 1, wherein the valve element (11, 31) is inserted inhydraulically shiftable valve drive members for activation of gasexchange valves in internal combustion machines.
 19. Valve arrangementaccording to claim 1, wherein the valve element (11, 31) is arranged ina tension medium clamping device which can be hydraulically activated.20. Valve arrangement according to claim 1, wherein the valve element(11, 31) is connected in a hydraulically actuated steering auxiliarysystem for vehicles.